Polo is a team sport played on horseback. The objective is to score goals against an opposing team. Players score by driving a small ball into the opposing team's goal using a long-handled mallet. The traditional sport of polo is played at speed on a large grass field up to 300 yards (274 meters) long by 160 yards (146 meters) wide (the size of nine football fields). Outdoor polo is played with a solid plastic ball; in arena polo, only three players are required per team and the game is played with a small air-filled ball, similar to a small soccer ball. The modern game lasts roughly two hours and is divided into periods called chukkas (also "chukkers").
A polo team consists of four mounted players. Each numbered position has certain responsibilities:
- Number One is the most offense-oriented player on the field, and also covers the opposing team's Number Four.
- Number Two has a vital role in offense, either running through and scoring, or passing to Number One; defensively, they cover the opposing team's Number Three, generally the other team's best player.
- Number Three is the tactical leader and must be a powerful hitter to feed balls to Number Two and One as well as maintaining defense.
- Number Four is primarily a defensive player. They can move anywhere on the field, but they usually try to prevent scoring, freeing their teammates for offense.
Polo mounts are called “ponies,” although the term “pony” is traditional and the mount is actually a full-sized horse. They range from 14.2 to 16 hands (58 to 64 inches) high at the withers, and weigh 900–1,100 pounds. The polo pony is selected for quick bursts of speed, stamina, agility and manoeuvrability. Temperament is critical: The horse must remain responsive under pressure and not become excited or difficult to control. They are trained to be handled with one hand on the reins, and to respond to the rider's leg and weight cues. A well-trained polo pony accounts for a great amount of the player's net worth to his team.
Polo players must have more than one pony, so tired mounts can be exchanged between or even during chukkas. A player's "string" of ponies may number two or three in Low Goal matches (with ponies being rested for at least a chukka before reuse), four or more for Medium Goal matches (at least one per chukka), and even more for the highest levels of competition.
Polo is actively played in 77 countries, but professionally in fewer countries, most notably Argentina, Australia, Brazil, Canada, Chile, the Dominican Republic, France, Germany, India, Iran, Jamaica, Mexico, New Zealand, Pakistan,Spain, Switzerland, the United Kingdom and the United States.
In the U.S., there are more than 275 polo clubs registered with the United States Polo Association with more than 4,500 members.
The world’s oldest active club is the Calcutta Polo Club, established in 1862.